Pink is a colour (rosa) and it is sometimes used to describe your cheeks – pink cheeks (sonrosados).
However, this article concerns “pink” as an idiom (modismo). Study these:
- Mr. Podemos´s Porsche is in the pink of condition (está en perfecto estado).
- Alejandro was tickled pink (estaba encantado) when Mrs. May became the British Prime Minister.
- The dish (el plato) was the pink of perfection (fue cocinado a la perfección).
If someone is “in the “pink” they are in good health.
So the next time you encounter an Englishman, and they ask after your health (how are you?) your reply could be “in the pink”.